Epstein-Barr virus (EBV) is a herpes virus that infects approximately 80% of individuals in Western societies. Following primary infection, a life long latent EBV infection of B cells is established. When primary infection is delayed until adolescence, which occurs in 10-20% of individuals in Western societies, there is an approximately 50% chance of developing infectious mononucleosis.
EBV has the very useful property of being able to "immortalise" or transform human B cells. These transformed B cells (referred to as LCLs) have the potential for essentially unlimited growth in the laboratory. There are two methods by which these LCLs can be established. Firstly, they may be established by the use of a common strain of EBV, referred to as B95.8. The LCL that is established is infected with this strain of virus. Secondly, LCLs may be generated using the latently infected B cells, present in all EBV immune individuals as a source of transforming virus. In this case, the LCL that emerges is transformed with the strain of EBV naturally present in any given EBV immune individual (referred to as spontaneous LCL).
There are two EBV types, A and B. The A type appears to predominate in the majority of lymphoid infections of healthy seropositive individuals. In such individuals, latently infected B cells appear to be controlled by CD8+ cytotoxic T cells (CTL) specific for the latent antigens, which include the EBV nuclear antigens (EBNAs) 2-6 and the latent membrane antigens (LMP) 1-3 (Moss, D. J. et al. 1992). Recent developments suggests that CD4+ CTL may also play a part in controlling this infection. These CTL are known to recognise short peptide epitopes derived from antigenic determinants in association with MHC class I molecules on the surface of an appropriate antigen presenting cell. LCLs displaying HLA class I and II alleles and presenting epitopes within EBV latent antigens are frequently used as a target cell for defining the specificity of CTL clones.
As whole virus or recombinant vaccines based on full length latent proteins are considered potentially oncogenic, an EBV vaccine based on CTL epitopes derived from the latent antigens is currently being developed (Moss, D. J. et al 1993). Khanna et al, (1992) have previously described several CTL epitopes.